Is often required to supply electricity to the consumer low voltage 220V. You can use an external adapter - but it’s bad, and to reduce the size of the device requires a power supply located in the device.
This 5v power supply used LM2995 to the converter circuit which can be connected directly to 220V. To do this, AC converted to DC voltage across the diode bridge VD1, and then lowered to 40V. Above 40 V we should not use it, due to the fact that the LM2995 maximum input voltage must not exceed 45V.
Transistors T1 and T2 form a pulsating stress amplitude up to 40V, which depends on the zener diode D1. This pulsating voltage is applied to the capacitor C1, which is slightly smoothed. Next on the chip down-converter output voltage is stabilized, defined applied chips : so for LM2575-5 5V it will be equal. Schottky diode D2, L1, C2 and C3 are the standard strapping of the chip.